President Trump said on Saturday that problems with a more than $14 million renovation project of the Lincoln Memorial Reflecting Pool had become so severe that it would likely have to be at least partly drained for “necessary repairs.”

He also blamed vandals, without offering evidence, and claimed that “multiple individuals” had been arrested.

The president’s announcement late Saturday, made on social media, was his starkest acknowledgment of the pool’s rapid deterioration in recent days. The water this week became covered by clouds of blooming algae, which were obscuring a floor that had just been painted a shade that Mr. Trump has called “American flag blue.” The paint then began to peel off, making it a tourist destination for unusual reasons.

Among those accused of vandalism was David Carter Hearn, 67, a cyclist and three-time Olympian as a canoeist who says he stopped at the site on Friday just to have a look, then reached down to touch a strip of peeling blue paint mixed with the algae.

The U.S. Park Police arrested Mr. Hearn shortly after, accusing him of destroying government property, a crime that can carry up to a 10-year prison sentence. Mr. Hearn denies the charge.

“I was just a curious, concerned citizen,” he said in an interview. “I guess I was there at the wrong place, wrong time.”